1. Field of The Invention
The present invention relates to an electrophotographic photoreceptor and, more particularly, to an electrical charge transporting layer of an electrophotographic photoreceptor having function-separation-type photoreceptor.
2. Description of the Related Art
In so-called function separation type photoreceptor the photosensitive region of an electrophotographic photoreceptor is separated into an electrical charge generating layer which generates electrical charge carriers by means of irradiation of light on a photosensitive layer, and an electrical charge transporting layer, which efficiently transports the electrical charge carriers which have been generated at the charge generating layer. Both organic and inorganic materials have so far been used as the electrical charge transporting layer. The organic material has been made, for example, by dispersing or dissolving a polymeric compound material such as polyvinylcarbazol, or a low-molecular-weight compound material such as pyrazoline or a triphenylamine, in a polymeric binding resin such as a polycarbonate. The inorganic material has been made, for example, of such substances as represented by a chalcogenide compound like selenium telluride or the like.
However, the life of an electrophotographic photoreceptor using such an electric charge transporting material is limited to thousands to tens of thousand of times of copying because of its unstable electrical repeatability (i.e., charge acceptance, dark decay, residual potential, and the like), and because of its tendency to peel and become scratched within the copying machine due to insufficient mechanical strength (i.e., hardness, adhesivity, and the like). Therefore, it is difficult to form an image which is stably repeatable over a long period of time. But, when a surface layer, a adhesive layer, or the like is provided to improve these weaknesses, the composition of the electrophotographic photoreceptor becomes complex and the generation of defects during the manufacturing process of the electrophotographic photoreceptor increases.
Further, an electrophotographic photoreceptor having a conventional organic electrical charge transporting material has insufficient electrical charge mobility. This can result in an electrophotographic photoreceptor which has unsatisfactory decay of the charge potential in low temperature environments and is unsuitable for high-speed copying operations.
Moreover, an electrophotographic photoreceptor having a conventional organic electrical charge transporting material has insufficient resistance to heat or light and suffers from crystallization or decomposition of low-molecular-weight materials. As a result, it is necessary to regulate the conditions or the environment in which the electrophotographic photoreceptor is to be used or kept.
Still further, in a conventional electrophotographic photoreceptor adopting a function separated type in which a charge transporting layer constitutes a part of the photo conductive layer, the charge transporting layer is generally thin. Therefore, absorption of light in the vicinity of the absorption region by the electrical charge generating layers is diminished and the quantity of light transmitted through the charge generating layers is increased. As a result, generation of interference fringes due to multiple reflections of the reflected light from the substrate are inevitable. This is especially true in printers utilizing infrared laser.